Heat exchanger

ABSTRACT

A heat exchanger connected to the smoke pipe of a central heating furnace below the horizontal plane of the smoke pipe and with an induced draft such that upon operation of the induced draft, the smoke pipe is blocked requiring the hot flue gasses to bypass through the heat exchanger and when the furnace operates without operation of the induced draft, the smoke pipe is open for direct flow of hot flue gasses.

finite States atent 1191 Wells 1 1 May 28, 1974 [54] HEAT EXCHANGER2,362,940 11/1944 Skerritt 165/166 3192 $28 211252 LZEZfiStf'. 1211 11 1Littleton, NH. 03561 i 1 Filed! Mal? 1973 Primary ExaminerWilliam E.Wayner Assistant Examiner-W. E. Ta olcai Jr. 21 A 1.N.:344829 P 1 1 pp 0Attorney, Agent, or Firm-Thomas N. Tarrant [52] 11.8. C1 237/55, 110/56,122/D1G. 1,

126/110 R, 165/38, 165/122 ABSTRACT [51] Int. Cl. F2411 7/04 A heatexchan ger connected to the smoke pipe of a [58] held of Search 237/55126/ 110/56 central heating furnace below the horizontal plane ofl22/DIG' 165/38 122 the smoke pipe and with an induced draft such thatupon operation of the induced draft, the smoke pipe is [56] ReferencesC'ted blocked requiring the hot flue gasses to bypass UNITED STATESPATENTS through the heat exchanger and when the furnace op- 1,720,5367/1929 Young 55/269 erates without operation of the induced draft, the1,785,334 12/1930 Black 122/D1G. I smoke pipe is open for direct flow ofhot flue gasses. 1,840,836 H1932 Davis, Jr..... 122/D1G. l 2,174,71010/1939 Wagner 237/55 10 Claims, 3 Drawing Figures HEAT EXCHANGERBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to heat exchangers and in particular to auxiliary heatexchangers for central heating units improving the efficiency of suchunits.

2. Relation to the Prior Art In the everlasting battle to decrease thecost and size of central heating installations, it has become a commonpractice to minimize the heat exchanger so that frequently a substantialportion of the generated heat passes wastefully up the chimney. In manyinstances, where space is available, it is economical to provide anauxiliary heat exchanger to absorb heat from the flue gasses of thesmoke pipe. Many such heat exchangers are known which surround and takeheat from the smoke pipe itself. U.S. Pat. Nos. 3,124,197; 2,468,909 and2,362,940 are exemplary. More effective compact heat exchangers requirea tortuous path for the flue gasses impeding and interfering with thedraft. To overcome the draft problem, an induced draft fan is known asdisclosed in US. Pat. No. 2,174,710.

When a tortuous path external to the furnace unit is provided for fluegasses, a number of safety hazards occur. Not only is the draft forproper operation of the burner likely to fail, but there is a muchgreater likelihood of dangerous leaks where the flue gasses may end upin living space.

SUMMARY OF THE INVENTION In accordance with the present invention, aheat exchanger has been provided bypassing a section of smoke pipe froma central heating furnace in which the heat exchanger lies below thehorizontal plane of the bypassed smoke pipe and the bypassed section ofsmoke pipe contains a damper. This damper is forced to the closedposition by operation of an induced draft device in the heat exchangerunit and opens during operation of the furnace when the induced draftdevice is not operating whereby normal flue draft is effective and theheat exchanger is effectively isolated from the flow of flue gasses inthe absence of induced draft. Thus, it is an object of the invention toprovide a novel auxiliary heat exchanger for central heating systems.

It is a further object of the invention to provide an induced draftsystem for an auxiliary heat exchanger in which the induced draft devicecoacts with a smoke pipe damper so as to place the heat exchanger in thepath of flue gasses only during operation of the induced draft.

Further objects and features of the invention will be better understoodafter reading the following description together with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation partially insection of a heat exchanger according to the invention.

FIG. 2 is a plan view in section along line 22 of FIG. 1.

FIG. 3 is a sectional view of the smoke pipe of FIG. 1 during heatingunit operation in the absence of induced draft.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention provides anauxiliary heat exchanger for a central heating system which bypasses asection of the furnace smoke pipe only during operation of the auxiliaryunit and substantially extracts the heat from the hot flue gasses beforethey pass up the chimney.

Thus, FIG. 1 depicts smoke pipe 10 connected to a furnace (not shown) atinlet end 11 and to a chimney flue (not shown) at output end 12.

Damper 14 is supported on pin 15 which in turn is mounted on bearings(not shown) in the walls of pipe 10. Pin 15 supports damper 14 offcenter being considerably closer to the upper edge of damper 14. Inorder that damper 14 may open fully even though suspended off center,damper 14 is made smaller in its transverse direction than the insidediameter of pipe 10 and flanges 16 and 17 are positioned around theinside circumference of pipe 10 to act as sealing flanges when damper 14is closed. Flange 16 is secured in the bottom circumference of pipe 10on the inlet side of damper 14 while flange 17 is secured to the upperportion of pipe 10 on the outlet side of damper 14. Flanges 16 and 17are discontinuous in the vicinity of pin 15 permitting damper 14 toswing through an arc of substantially Adjustable balance weight 18 iscentrally located in damper 14 above pin 15 for adjusting the balance ofdamper 14 to open under conditions of normal operating draft. Auxiliaryheat exchanger 20 is connected to smoke pipe 10 through downpipe 21 onthe inlet side of damper l4 and through induced draft pipe 23 isconnected to smoke pipe 10 on the outlet side of damper 14. Downpipe 21makes a tee connection with pipe 10 at its upper end and connects toinlet 22 of heat exchanger 20 at its lower end. Inlet 22 is a passage tothe bottom of heat exchanger 20 connecting to open ends of a pluralityof vertically positioned cylindrical tubes 24. First plurality ofcylindrical tubes 24 is depicted as 1! tubes shown in FIG. 2. The bottomends of tubes 24 are supported in spaced relationship and spaces betweenthem are blocked by sealing plate 25. A supporting partition 26terminates inlet passage 22 so that any incoming hot flue gasses mustpass vertically upward through tubes 24. The upper ends of tubes 24 arespaced below the upper surface of heat exchanger housing 27 andsupported in spaced relation by sealing plate 28. Tubes 24 open at theirupper ends into space 30 between housing 27 and sealing plate 28. Space30 is open to the upper ends of tubes 24 and also the upper ends ofsecond plurality of tubes 31. Space 30 is terminated by a supportingseal 32 so that flue gasses passing upward through tubes 24 must in turnpass downward through tubes 31.

Referring to FIG. 2 it will be seen that tubes 31 are a second pluralityof vertically positioned cylindrical tubes depicted as 11 tubes. Thebottom ends of tubes 31 open into a further space 34 which is continuousacross the open bottom ends of third plurality of vertically positionedcylindrical tubes 35. The bottom ends of tubes 31 and tubes 35 aresupported in spaced relationship by sealing plate 36. Space 34 is anenclosed space such that hot gasses passing downwardly through tubes 31must pass upwardly through tubes 35. Referring again to FIG. 2 it willbe seen that tubes 35 are also depicted as 11 tubes. Space 37communicating with the upper ends of tubes 35 is connected to induceddraft blower 38 by passage 40. Tubes 35 are supported in spaced.relation at their upper ends by a sealing plate 41.

Baffle 42 supported adjacent opening 44 between passage 40 and space 37serves to improve dynamic flow of gasses into passage 40.

Blower 38 suitably of the squirrel cage electrically driven type isconnected to pull gasses through passage 40 driving them through induceddraft pipe 23 into smoke pipe 10. induced draft pipe 23 is depicted asangled toward outlet 12 of pipe at its connection point with pipe 10.The angle of this pipe will be discussed further in connection with theoperation of the heat exchanger.

Second blower 45 has an intake opening 46 into ambient space around theheat exchanger. An air filter (not shown) is desirably positioned acrossthis opening to filter out dust and opening 46 may be connected tooutdoors or some other location as desired. Blower 45 is depicted inFIG. 2 as connected to a side wall 47 of heat exchanger and blows intopassages around tubes 24, 31 and to carry heat from the tubes. Lookingat the sectional plan view in FIG. 2 it will be seen that blower blowsair in past and around the third plurality of tubes 35. A baffle 50separates tubes 35 from tubes 31 extending from wall 47 to a positionshort of opposite wall 51 so that the air from blower 45 must pass byand around tubes 35 before encountering tubes 31 after passing aroundthe end of baffle 50. A second baffle 52 separates tubes 24 from tubes31 extending the confined circuitous travel of the air from blower 45 sothat it is'forced by and around tubes 31 and then tubes 24 beforereaching outlet 54 in wall 51. Outlet 54 is suitably connected to aregister for providing heated air into the immediately adjacent space ormay be connected to ducting so as to provide heated air at a distantlocation.

The number and diameter of tubes 24, 31 and 35 is determined so as toprovide efficient flow of flue gasses. However, the efficiency of heattransfer is determined by the area of exposed metal surface of the tubesfrom which the heat is picked up by air passing from blower 45 to theoutlet 54. For a more compact design than that depicted, fewer tubes ofa larger diameter may be utilized or merely a shorter length of tubinghaving the same diameter with fins extending from the tubing wallsnormal to the axis of the tubing so as to increase thermal transfer.

In any kind of a combustion heating system a draft which provides aconstant flow of air for combustion purposes and carries the wasteproducts of combustion away is of significant importance. Commonly thedraft is based upon the fact that hot gasses are lighter in weight thancold gasses and therefore rise. Accordingly, if a gas such as air isheated at the bottom of a vertical duct (i.e., chimney flue) and a muchcolder air exists at the top of the duct, the heated air will risethrough the duct causing a draft.

Thus, when a furnace is ignited at the bottom of a vertical chimneyflue, a definite pressure differential occurs between the combustiongasses in the furnace and the relatively cold air at the top of thechimney causing a dynamic flow. This is well known and in FIG. 1 willcause damper 14 in smoke pipe 10 to open under the pressure differentialtending to allow the hot gas from the furnace entering at inlet 1 l topass through on to outlet 12 and up the chimney. Damper 14 can beadjusted in balance by weight 18 either so that it will be normally openunder residual draft that exists even when the furnace is not operatingor so that it remains just barely closed to open on the smallestincrease in heat on the furnace side. This latter is considered to bethe preferred condition since it reduces loss of warm air up the chimneywhen the furnace is quiescent. However, on operation of blower 38, airor flue gas is pulled through the heat exchanger through inlet passage22 and connecting pipe 21 producing a low pressure zone on the inletside of pipe 10. At the same time, air and/or flue gasses are forcedthrough draft pipe 23 into the outlet side of pipe 10 increasing thepressure in the outlet side of the pipe. Thus a pressure differential isproduced across damper 14 forcing the damper closed. With damper l4closed, all flue gasses must pass through heat exchanger 20. Thus asdepicted in FIG. 1, low and high pressure zones produced by the induceddraft means 38 operate damper 14. Some angling of pipe 23 is desirablefor efficient utilization of induced draft means 38. Since thearrangement of draft means 38 tends to affect pressure on both sides ofdamper 14 simultaneously, any venturi effect is unlikely. Nevertheless,pipe size relationships, angles and opening characteristics must bedesigned to avoid venturi action. I

It will be recognized that other electrical or mechanical interlockmeans may be used to provide coaction between damper l4 and induceddraft means 38. For example, the switch operating the electric motivepower for induced draft means 38 may operate a solenoid actuating damper14 from its closed to its open position. It will be recognized that thissame switch during the heating season of the year would normally beinterlocked with a switch operating the heating furnace or else evenmore desirably with a thermal switch reacting to the temperature of thesmoke pipe. Additional thermostatic means could also be interconnectedto avoid heat being providedin excess of a desired room temperature.

In the event that induced draft means 38 does not operate, heatexchanger 20 would be effectively isolated from the smoke pipe sincedamper 14 would open pro viding a more direct flow of flue gasses duringoperation of the furnace.

While the invention has been described with relation to a specificembodiment, it will be seen that a number of variations are availableand are contemplated as within the scope of the invention to the extentcovered by the appended claims.

I claim:

1. A heat exchanger forinsertion in the smoke pipe of a central heatingunit between the heating unit and a chimney flue therefore comprising:

a. A direct smoke pipe connection for connecting the smoke flue of acentral heating unit to a chimney flue;

b. A damper in said direct smoke pipe;

c. A plurality of smoke passages supported in spaced relationship withinan enclosure;

d. A smoke passage connected to said direct smoke pipe upstream of saiddamper and to said plurality of smoke passages;

e. Induced draft means connected between said plurality of smokepassages and said smoke pipe downstream of said damper characterized inthat operation of said induced draft means causes said damper to close;and,

f. Means to provide a flow of a heat distributing medium through saidenclosure past said plurality of smoke passages for absorbing heat anddistributing it.

2. A heat exchanger according to claim 1 wherein said damper is normallyopen.

3. A heat exchanger according to claim 1 wherein operation of saidinduced draft means produces a pressure differential in said smoke pipeacross said damper causing it to close.

4. A heat exchanger according to claim 1 wherein said direct smoke pipeis in a substantially horizontal position entirely above said pluralityof smoke passages.

5. A heat exchanger according to claim ll wherein said induced draftmeans is a blower.

6. A heat exchanger according to claim ll wherein said means to providea flow of heat distributing medium is a blower to provide a flow of air.

7. An auxiliary heat exchanger for a furnace in combination with andbypassing a direct section of smoke pipe for connection between afurnace and a chimney flue comprising:

a. A damper in said direct section of smoke pipe;

b. An inlet passage connected between said smoke pipe and said heatexchanger on the furnace side of said damper;

c. An outlet passage connected between said heat exchanger and saidsmoke pipe on the chimney side of said damper;

d. A plurality of spaced flues connecting said inlet passage with saidoutlet passage as heat exchanging elements; and

e. Induced draft means for said heat exchanger coacting with said dampereffecting closure of said damper upon operation of induced draft through7 said heat exchanger.

8. An auxiliary heat exchanger according to claim 7 wherein said induceddraft means is a blower located in said outlet passage.

9. An auxiliary heat exchanger according to claim 7 wherein said induceddraft means coacts with said damper by placing a pressure differentialacross said damper effecting closure thereof.

10. An auxiliary heat exchanger according to claim 7 wherein said spacedflues are positioned vertically within an enclosure and air iscirculated through said enclosure around said spaced flues and out as aspace heating medium.

1. A heat exchanger for insertion in the smoke pipe of a central heatingunit between the heating unit and a chimney flue therefore comprising:a. A direct smoke pipe connection for connecting the smoke flue of acentral heating unit to a chimney flue; b. A damper in said direct smokepipe; c. A plurality of smoke passages supported in spaced relationshipwithin an enclosure; d. A smoke passage connected to said direct smokepipe upstream of said damper and to said plurality of smoke passages; e.Induced draft means connected between said plurality of smoke passagesand said smoke pipe downstream of said damper characterized in thatoperation of said induced draft means causes said damper to close; and,f. Means to provide a flow of a heat distributing medium through saidenclosure past said plurality of smoke passages for absorbing heat anddistributing it.
 2. A heat exchanger according to claim 1 wherein saiddamper is normally open.
 3. A heat exchanger according to claim 1wherein operation of said induced draft means produces a pressuredifferential in said smoke pipe across said damper causing it to close.4. A heat exchanger according to claim 1 wherein said direct smoke pipeis in a substantially horizontal position entirely above said pluralityof smoke passages.
 5. A heat exchanger according to claim 1 wherein saidinduced draft means is a blower.
 6. A heat exchanger according to claim1 wherein said means to provide a flow of heat distributing medium is ablower to provide a flow of air.
 7. An auxiliary heat exchanger for afurnace in combination with and bypassing a direct section of smoke pipefor connection between a furnace and a chimney flue comprising: a. Adamper in said direct section of smoke pipe; b. An inlet passageconnected between said smoke pipe and said heat exchanger on the furnaceside of said damper; c. An outlet passage connected between said heatexchanger and said smoke pipe on the chimney side of said damper; d. Aplurality of spaced flues connecting said inlet passage with said outletpassage as heat exchanging elements; and e. Induced draft means for saidheat exchanger coacting with said damper effecting closure of saiddamper upon operation of induced draft through said heat exchanger. 8.An auxiliary heat exchanger according to claim 7 wherein said induceddraft means is a blower located in said outlet passage.
 9. An auxiliaryheat exchanger according to claim 7 wherein saId induced draft meanscoacts with said damper by placing a pressure differential across saiddamper effecting closure thereof.
 10. An auxiliary heat exchangeraccording to claim 7 wherein said spaced flues are positioned verticallywithin an enclosure and air is circulated through said enclosure aroundsaid spaced flues and out as a space heating medium.